This invention generally relates to a brake actuator assembly, and specifically to a brake actuator assembly including a sensor for monitoring clearance between a friction element and a rotating member.
Conventional brake assemblies include an actuator for moving a friction element into contact with a rotating member. Typically, an actuator drives the friction element from a home position into contact with the rotating member. Wear of the friction element increases the distance that the friction element must move to contact the rotating member. The increased distance is typically accommodated by mechanical devices that compensate for friction element wear by adjusting a home position closer to the rotating member.
A known brake actuator includes a push rod movable in response to changes in air pressure within an air chamber. The push rod includes a hollow inner cavity for a biasing spring. Movement of the push rod is transmitted through the biasing spring to an insert. Movement of the insert causes movement of an operating shaft. The operating shaft in turn moves mechanical linkage that drives brake pads toward engagement with a rotor.
Once the brake pad contacts the rotor, the push rod overcomes the biasing spring and contacts the insert forming a solid linkage. As the brake pad wears, displacement of the push rod must also increase to compensate. The displacement of the push rod corresponds to movement of the brake pad. Therefore, clearance between the brake pad and the rotor corresponds to the displacement of the push rod.
Current brake actuators measure displacement of the push rod with a mechanical switch indicating clearance between the brake pad and the rotor. A controller adjusts the initial home position between the rotor in view of the measured clearance between the brake pad and the rotor in order to maintain consistent braking force throughout the useful life of the brake pad.
Disadvantageously, mechanical switches provide only limited accuracy and dependability. Further, mechanical switches require specific actuation features on brake member components, and are difficult to adapt to different actuator assemblies.
Accordingly, it is desirable to design an accurate, adaptable method and device for determining clearance between a friction element and a rotating member.